This invention relates generally to improvements in check valves, and more particularly, but not by way of limitation, to fluid flow-actuated check valves suitable for use in float collars, float shoes or other casing equipment in well cementing operations.
When casing is inserted into a well bore, it is subsequently fixed and supported therein by an operation known as primary cementing. Cement is forced down the bore of the casing, through an aperture in the guide shoe at the bottom of the casing, and up the annulus surrounding the casing and between the casing and the well bore to the desired level. One or more valves, commonly termed float valves, are installed in the casing to prevent back flow of the cement into the casing from the annulus if pressure in the casing is reduced. Such a float valve may be in the form of a collar or an integral part of the guide shoe. The closed float valve or valves also seal the bottom of the casing and prevent fluids in the well bore from filling it when the casing is lowered into the well bore, thus providing buoyancy in the casing and reducing total weight supported by the rig derrick. Illustrative of this type of float valve are the Halliburton float collar with Super Seal valve and the Super Seal valve float shoe, depicted on pages 2433 and 2434, respectively, of Halliburton Services Sales and Service Catalog No. 43. After the casing is in place in the well bore, a bottom cement plug may be pumped before the cement, in order to displace any fluid in the casing, down through the casing to seat above the uppermost float valve, at which point pressure is increased in the casing, a diaphragm in the bottom plug is ruptured, and cement flows through the bottom plug, opening the float valve or valves by overcoming its biasing mechanism. The cement then travels to the well bore annulus, as previously described. A top plug follows the cement, and is pumped down the casing bore to seat on the bottom plug, at which point the back pressure from the cement in the casing below the float valve and in the well bore annulus is supposed to close the valve.
While many types of float valves other than the Halliburton poppet-type Super Seal valve are currently known in the art (for example, flapper type or ball type valves), it is believed that a poppet-type valve provides exceptionally reliable operation. A problem with prior art poppet-type valves of the Super Seal type, however, is that they are more expensive to manufacture than other type float valves, both due to the number of parts required for the valve assembly as well as the overall length of the valve assembly alone and as it is normally employed in a section of casing equipment, maintained therein by a cement sheath extending between the outside of the valve assembly and the inside of the casing equipment section. This cement is used not only to seal between the valve assembly and the casing equipment section, but also to support the valve assembly against pressure exerted by cement or other fluid below the valve assembly as a result of hydrostatic pressure in the casing/well bore wall annulus.